The Swirling Orifice Plate: A Flowmeter for All Reasons

Abstract

The orifice plate flow meter is the most common form of differential pressure flow meter used in industry. The standard discharge coefficient, which is defined by both British Standard and ISO 5167, is only valid if the flow approaching the meter is perfectly settled and fully developed. However, in practical applications the flow approaching the orifice meter is often disturbed by pipe-fittings and consequently the measurements become inaccurate. Basically, the design of the orifice plate meters that are independent of the upstream disturbances is a main goal for orifice plate metering. This task can be achieved either by using a long straight settling length upstream and downstream of the orifice plate or using a flow conditioner upstream of an orifice plate. In addition, the standard orifice plate is vulnerable when metering dirty flow due to the accumulation of dirt in front of the orifice plate which can alter the accuracy of metering as well. In this paper the effect of the swirler flow conditioner for both standard and non-standard flow conditions has been investigated in an experimental rig and validation of the results has been justified with the appropriate CFD domains. In these investigations the effect of different designs of swirler flow conditioners have been examined in asymmetric and swirling flow profiles. The results so far show the cone swirler flow conditioner has a desirable effect for both asymmetric and swirling flow disturbances. They also show the error of metering for non-standard velocity profiles with the swirler flow conditioner is typically 1.5% compared to around 4% for a standard orifice plate. Moreover using a swirler conditioner tends to keep particles in suspension and thus prevents the accumulation of dirt particles in front of orifice plate. All experimental and numerical results here are presented for different velocity profiles both swirling and asymmetric profiles, mass flow rates and for β = 0.5.